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Author Topic: 48.048kHz and 88.2kHz ???  (Read 8275 times)

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Offline Brian

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Re: 48.048kHz and 88.2kHz ???
« Reply #15 on: April 21, 2005, 09:32:10 PM »
I just fed mine a 88/16 signal - the resulting playback is half speed...

As it recorded..the JB3 displayed 44.1 as the sample rate...

yeah....cause it resampled ;)

Why do you think it resampled?

because it was made by creative labs with a non-bit transparant AD at those levels.

hexyjones

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Re: 48.048kHz and 88.2kHz ???
« Reply #16 on: April 21, 2005, 09:34:12 PM »
Im using an outboard AD...optical in

Offline Brian

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Re: 48.048kHz and 88.2kHz ???
« Reply #17 on: April 21, 2005, 09:34:53 PM »
Im using an outboard AD...optical in

yes i know.  it resampled the digital input.

hexyjones

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Re: 48.048kHz and 88.2kHz ???
« Reply #18 on: April 21, 2005, 09:35:45 PM »
Im using an outboard AD...optical in

yes i know.  it resampled the digital input.

resampled it to what?

Offline Brian

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Re: 48.048kHz and 88.2kHz ???
« Reply #19 on: April 21, 2005, 09:36:51 PM »
44.1 apparantly

hexyjones

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Re: 48.048kHz and 88.2kHz ???
« Reply #20 on: April 21, 2005, 09:38:52 PM »
Then why does it play half speed - ?

answer: it doesnt resample...

I bet the JB3 firmware just guessed the sample rate - probably has no programming to actually display "88.2"

Offline Brian

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Re: 48.048kHz and 88.2kHz ???
« Reply #21 on: April 21, 2005, 09:39:28 PM »
i'm guessing the output is resampling?  i didin't see your post about half speed, sorry.

hexyjones

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Re: 48.048kHz and 88.2kHz ???
« Reply #22 on: April 21, 2005, 09:45:25 PM »
Ok - I transferred the track to my computer...

Opened in SF7 - Went to "Properties" and changed the sample rate to 88.2 (i think this might just change the header)

Now it plays normal speed...

Offline Brian

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Re: 48.048kHz and 88.2kHz ???
« Reply #23 on: April 21, 2005, 09:48:30 PM »
do you have an fft to measure all the frequencies you are getting?  what did you record?

hexyjones

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Re: 48.048kHz and 88.2kHz ???
« Reply #24 on: April 21, 2005, 09:55:07 PM »
I ran the analog out of an MD player into my Behringer Ultramatch A/D which was set to 88/16

Basically just grabbed the closest noisemaker...

Whats fft?

I can set up a better test...

Offline dklein

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Re: 48.048kHz and 88.2kHz ???
« Reply #25 on: April 22, 2005, 01:10:50 AM »
I just fed mine a 88/16 signal - the resulting playback is half speed...

As it recorded..the JB3 displayed 44.1 as the sample rate...

yeah....cause it resampled ;)

No it didn't actually.  The sample rate is nothing more than header info used for playback - how fast should it consume samples.  When recording thru optical in, the JB3 just writes data as it comes in.  It's not resampled or reclocked to anything.  Every sample is written, unless you feed it too quickly, in which case it drops samples.  I tested 96k and the JB3 could not keep up, but it's possible that it could keep up at 88.2 (doubtful but possible).
KM 184 > V2 > R4
older recording gear: UA-5  / emagic A62 / laptop / JB3 / CSB / AD20 / Sharp MT-90 / Sony MDS-JE510
Playback: Pioneer DV-578 > Lucid DA 9624 >many funny little british boxes > Linn Isobarik PMS

Offline Ed.

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Re: 48.048kHz and 88.2kHz ???
« Reply #26 on: April 22, 2005, 05:02:39 AM »
if it does do 88.2 successfully, what really is the point?  its hard to tell 48khz from 96khz in the 24 bit world (for most folks anyway), i'd imagine telling 88.2 from 44.1 in the 16 bit world wouldn't really be that evident.
« Last Edit: April 22, 2005, 06:18:21 AM by Ed Swearengen »


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Offline Stuart

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Re: 48.048kHz and 88.2kHz ???
« Reply #27 on: April 22, 2005, 05:44:37 AM »
Like somebody else said, the seemingly strange sample rates of some of the more professional boxes are meant to deal with "pull up" and "pull down" situations encountered in post production.  On a film shoot, most people shoot (record) audio at 30 fps, with a set time code generator acting as the master.  The camera operates at 24 fps.  During telecine, in order to frame-match NTSC video speed, both the camera and the audio need to be slightly slowed down in order to sync.  That's what gives the .01% difference.  Now, you may ask, why would you record at 48.048k or 44.156 when you're pulling down in post-production.  The answer is that for movies t hat are never going to be re-released in theaters that it's easier to just record audio at just slightly faster than film speed, knowing all along that the final output will end up at video speed (.01% slower again) and be more compatible with most editing systems.

   In other words, if you shoot a movie at 48.048, you don't need to pull down to 47.952Hz during the editorial process.  You can, instead, submit video-speed  audio that will enable just about anybody to work on the movie without the need of high-end equipment (TDM Pro-Tools, or Nuendo with Timelock and Blackburst).  If you have any questions about this crap, please email me at stuart@soundbreeder.com


 

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